The 315-year-old instrument was taken from internationally acclaimed violinist Min-Jin Kym as she ate in Pret a Manger with her cellist boyfriend in Euston station in 2010.

The violin, along with a Peccatte bow worth £62,000, was swiped from the floor by Irish traveller John Maughan – working with two teenage accomplices – while Ms Kym was on the phone.

Despite researching the violin online, Maughan, 41, was so ignorant of its value that he offered it to a stranger in an internet café for just £100. But the man turned down the offer claiming that his daughter already owned a recorder.

Maughan was jailed for four and a half years at Blackfriars Crown Court in 2011 for stealing the 1698 violin – one of only 450 in the world.

But now police believe the violin may have turned up in Bulgaria after undercover detectives were offered a Stradivarius for £250,000 from an alleged gipsy crime boss.

Only three of the rare violins are known to be missing and police say there is a strong possibility it is the one that disappeared from Euston.

The British Transport Police confirmed they were investigating whether the violin belongs to Ms Kym.

A spokeswoman said: "We're trying to establish with the underwriters and international colleagues the instrument's background."

Ms Kym, who is signed to record label Sony BMG, began playing the violin at the age of six and made her international debut with the Berlin Symphony Orchestra when she was 13.

At 16, she became the youngest student ever to be awarded a Foundation Scholarship at the Royal College of Music and went on to study with the violin virtuoso Ruggiero Ricci who said she was “the most talented violinist I have ever worked with”. She has also played with the Royal Philharmonic Orchestra.

He said: "This isn't a female with a monumental amount of money. This is her life, her profession.

"She is one of the top violinists in the world and she has this instead of a house, instead of a car and she gets to a violin of this value by trading up as one would a mortgage as she's become more successful"